1. Field of the Invention
This invention relates generally to nanotubes and nanoparticles and more specifically to nanotubes and nanoparticles containing boron, carbon and nitrogen.
2. Description of Related Art
Carbon nanotubes were discovered by S. Ijima (Nature, 354:56, 1991) and synthesized by T. W. Ebbesen and P. M. Ajayan (Nature, 358:220, 1992). Theoretical studies by N. Hamada, et al. (Phys. Rev. Lett., 68:1579, 1992) and M. S. Dresselhaus, et al. (Solid State Commun., 84:201, 1992) showed that carbon nanotubes exhibit either metallic or semiconducting behavior depending on the radii and helicity of the tubules. Hamada proposed a notation to classify the helicity using the indices (n,m). The (n,m) tubule is obtained by rolling a planar graphite sheet so that a first hexagonal carbon ring on one edge of the sheet will connect with a second hexagonal carbon ring, which in the planar configuration was separated from the first ring by nA.sub.1 +mA.sub.2 ; where A.sub.1 and A.sub.2 are primitive translation vectors on the graphite sheet.
The carbon nanotubes have interesting and potentially useful electronic and mechanical properties. Among the barriers to actualizing the utility of carbon nanotubes are nonuniform electronic properties resulting from small band gaps.
A turbostratic tubular form of boron nitride (BN) having a diameter on the order of 1 to 3 micrometers was produced from the amorphous phase of BN (E. J. M. Hamilton et al., Science, 260:659, 1993). Hamilton's micron-scale, amorphous phase, BN tubes are characterized by a random, non-crystalline arrangement of atoms in the wall of the tube; the atomic arrangement does not map back on itself. Limitations of BN amorphous phase tubes, not having a high degree of crystallinity in the tube walls, include reduced mechanical strength, and ill-defined and unpredictable electronic properties, compared to tubes having a crystalline structure. Another characteristic of Hamilton et al.'s amorphous BN tubes is their size, on the order of 1000 times larger than nanoscale structures. Because BN is not an electrical conductor Hamilton et al. synthesized their amorphous micron-scale tube using a high temperature gas reaction instead of an arc system.
Theoretical studies by N. Hamada, et al. (Phys. Rev. Lett., 68:1579, 1992) and M. S. Dresselhaus, et al. (Solid State Commun., 84:201, 1992) showed that carbon nanotubes exhibit either metallic or semiconducting behavior depending on the radii and helicity of the tubules. Hamada proposed a notation to classify the helicity using the indices (n,m). The (n,m) tubule is obtained by rolling a planar graphite sheet so that a first hexagonal carbon ring on one edge of the sheet will connect with a second hexagonal carbon ring, which in the planar configuration was separated from the first ring by nA.sub.1 +mA.sub.2 ; where A.sub.1 and A.sub.2 are primitive translation vectors on the graphite sheet.
Carbon nanotubes have small bandgaps that make their electronic properties nonuniform. In addition, the bandgap of a carbon nanotube is relatively sensitive to tube diameter, helicity, and multiplicity of walls. Furthermore, it is difficult to dope carbon nanotubes, that is to add small concentrations of non-carbon material to the tubes. Typically doping occurs at concentrations of about 1% or less.